[R] assign if not set; stand-alone R script, source'able too?

[Marc Schwartz]

Alexy,

In addition to Gabor's reply, you might want to review the following
page from the R Wiki:

http://wiki.r-project.org/rwiki/doku.php?id=developers:rinterp

which covers LittleR by Jeff Horner and Dirk Eddelbuettel and provides
shell scripting support for R.

HTH,

Marc

On Mon, 2007-11-19 at 20:56 -0500, Gabor Grothendieck wrote:
> Here are two solutions:
> 
> # 1
> "%or%" <- function(x, y) if (is.na(x)) y else x
> NA %or% 1 # 1
> 3 %or% 1 # 3
> 
> # 3
> # can omit Negate<- line in R 2.7.0 since its predefined there
> Negate <- function(f) function(...) ! match.fun(f)(...)
> Filter(Negate(is.na), c(NA, 1))[1] # 1
> Filter(Negate(is.na), c(3, 1))[1] # 3
> 
> 
> On Nov 19, 2007 8:22 PM, Alexy Khrabrov <deliverable at gmail.com> wrote:
> > Marc -- thanks, very interesting.
> >
> > I was in fact tinkering at a very simple default arguments assignment
> > to a generic command-line R script header:
> >
> > #!/bin/sh
> > # graph a fertility run
> > tail --lines=+4 "$0" | R --vanilla --slave --args $*; exit
> > args <- commandArgs()[-(1:4)]
> >
> > # the krivostroi library
> > source("/w/ct/r/kriv/krivostroi.r")
> >
> > # NB: vector assignment in R? defaults?
> > file    <- args[1]
> > maxruns <- if (is.na(args[2])) 1 else args[2]
> > prefix  <- if (is.na(args[3])) file.basename(file) else args[3]
> >
> > -- turns out, args[N] here are NA if not supplied on the command-
> > line.  I'd like to see a nicer way to do it still, without repeating
> > args[N] twice for each assignment though.
> >
> >
> > Another thing from this snippet, unrelated to assignment, is that was
> > the only way to get R script to be packed in a single file runnable
> > from the command line in a stand alone way.  Yet when I want to source
> > () it, R obviously chokes on the shell command tail.  My previous
> > solution was to have a pair of files, script.r/script.sh for each R
> > script, where .sh would look like
> >
> > echo "argv <- c('$1','$2'); source('main.r')" | R --vanilla --slave
> >
> > Wonder if there's a way to have a single file which is a stand-alone
> > command script, and can be source()'d in R.
> >
> > Cheers,
> > Alexy
> >
> > On Nov 20, 2007, at 4:03 AM, Marc Schwartz wrote:
> > >
> > > On Tue, 2007-11-20 at 03:32 +0300, Alexy Khrabrov wrote:
> > >> What's the idiom of assigning a default value to a variable if it's
> > >> not set?  In Ruby one can say
> > >>
> > >> v ||= default
> > >>
> > >> -- that's an or-assign, which triggers the assignment only if v is
> > >> not set already.  Is there an R shorthand?
> > >>
> > >> Cheers,
> > >> Alexy
> > >
> > > If 'v' is not set, then it does not exist, hence you can use exists
> > > () to
> > > check for it. However, you need to [potentially] distinguish where the
> > > variable might be located. Keep in mind that R uses lexical scoping,
> > > hence the exists() function has other arguments to define where to
> > > look.
> > >
> > > A simple example:
> > >
> > >> v
> > > Error: object "v" not found
> > >
> > > if (!exists("v")) v <- "Not Set"
> > >
> > >> v
> > > [1] "Not Set"
> > >
> > > v <- "Set"
> > >
> > > if (!exists("v")) v <- "Not Set"
> > >
> > >> v
> > > [1] "Set"
> > >
> > >
> > > See ?exists for more information.
> > >
> > > That being said, just as an example of extending R, you could do the
> > > following, which is to create a new function %||=% (think %in% or %*%)
> > > which can then take two arguments, one preceding it and one following
> > > it, and then basically do the same thing as above. Again here, scoping
> > > is critical.
> > >
> > >
> > > "%||=%" <- function(x, y)
> > > {
> > >   Var <- deparse(substitute(x))
> > >   if (!exists(Var))
> > >     assign(Var, y, parent.frame())
> > > }
> > >
> > >> v
> > > Error: object "v" not found
> > >
> > > v %||=% "Not Set"
> > >
> > >> v
> > > [1] "Not Set"
> > >
> > > v <- "Set"
> > >
> > > v %||=% "Not Set"
> > >
> > >> v
> > > [1] "Set"
> >
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.